GHGT-10 : Assessing the integrity of fault- and top seals at CO2 storage sites

Induced stress changes due to CO2 injection into geological reservoirs can mechanically damage bounding fault- and top seals creating preferential pathways for CO2 migration from the containment or trigger existing faults causing seismic activity at storage sites. In this paper we present geomechanical simulations of the poro-mechanical effects, thermal and chemical effects of CO2 injection on the integrity of fault- and top seals. Simulation work was performed as part of recent feasibility studies for geological CO2 storage in a depleted gas field and a saline aquifer in the Netherlands. Poro-mechanical and thermal effects were investigated using site-specific finite element and finite difference models as well as (semi-)analytical methods. Long term chemical effects were investigated using generic discrete element models of a representative anhydrite caprock sample. The analysis show that (1) geomechanical numerical models can be used to define clear criteria for maximum admissible pressure build-up during CO2 injection to prevent caprock fracturing, shearing of pre-existing fractures and fault reactivation, (2) combined poro-elastic and thermal effects of CO2 injection may induce fracturing in the near-well area, (3) long term chemical reactions of anhydrite caprock with CO2-rich fluids may cause significant reduction in failure strength at timescales of ~50000 years